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Do the RS400, RS420, RS440 Entry Level Projectors Lack the Lamp Iris?

I had great results boosting the contrast ratio of an old RS45 entry level projector by adding a lamp iris as detailed first in the german forum. It was a simple project that made a dramatic difference in projected image transparency and only cost about 20% light output.

Here is my iris for the RS45... Easy to make out of aluminum flashing. I would rank it as a must-do for the mod'er in us. Well out of warranty now, but able to get very noticeable jump up in picture quality for under two hours of tinkering. Might even be better with a 16:9 shaped aperture, but I have not tested that.

Do the entry level RS400, RS420, RS440 projectors also lack the lamp iris of their middle and top level siblings?

« Last Edit: July 03, 2021, 06:07:07 AM by Guy Kuo »

Did trial with 36 x 20 mm aperture. Reduces light output considerably for same area opening and also loses the sharpening/reduced scatter effect that I noticed with the 27 mm square aperture. I would recommend staying with a square aperture rather than a wider aspect opening.

The improved contrast and deeper black is enough to make THX Eclipse look satisfying. Whereas before, the black background glowed just enough to be distracting. It's not perfect black, but much closer than stock.

Attached is cleaner dimensional drawing for 27 mm aperture "lamp iris" for RS-45

BTW a wood chisel, wooden plank, and hammer make cutting out the aperture opening trivial.
« Last Edit: July 03, 2021, 08:04:49 PM by Guy Kuo »

Finalized my lamp "iris" at 27 mm square with flat black surface facing away from lamp and polished surface facing lamp. The blacking was to reduce light scatter in direction of imaging elements. The polished side was to reduce energy absorption and recycle some rejected light. I am quite delighted with the results. Projector has never looked this good.

Blacking was done with flat, high temp barbecue paint. Heat gun treated and then baked 12 hours to remove paint volatiles.

Polished side was sanded and then polished to near mirror finish.



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That's a great mod. I need an old projector to try this - not that I have the spare time. 
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If this is the same Guy Kuo who was associated with Avia, I appreciated that calibration disc back in the day!

Yes. It's one and the same.
Two decades ago! How the time flies. Been pulled away from HT doing medical projects. 

Going to a black / mirrored version of the 27 mm iris has a more pronounced deepening of black than expected. I thought there would be a little back scatter to absorb, but what I'm seeing is a lot more darkening of black than that would understand. Then I remembered that LCOS is unlike DLP or LCD in how it disposes of unwanted light. DLP directs light into a light trap. LCD absorbs the light in the LCD panel. LCOS directs "black state, S-polarized light back towards the lamp through the wire grid beam splitter. Guess what is now in the return path towards the lamp? A nice black light trap surrounding a 27 mm aperture. That means more efficient disposal of unwanted light.

In other words, LCOS has an additional mechanism for a black lamp iris to reduce rejected light. Not only is contrast improved by reducing the acceptance aperture to reduce inbound, non-perpendicular light rays, but blacking the LCOS facing (away from lamp) side of a lamp iris can potentially absorb rejected light that is being reflected back for disposal.

The one picture I have found of the JVC lamp iris mechanism indicates the OEM iris is not black colored on its LCOS panel facing side. It will be a good experiment to see if blacking that side of the OEM lamp iris further deepens the black of the more premium models equipped with an OEM lamp iris.

« Last Edit: July 09, 2021, 05:10:11 PM by Guy Kuo »

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